The present invention generally relates to the field of medical devices, and more particularly, to the field of catheters such as guide catheters used for the placement of medicines and medical devices within the body and diagnostic catheters used to inject radiopaque fluids within the body for treatment and diagnosis of vascular diseases. Specifically, the invention is directed to a catheter tube, particularly useful in intravascular guide catheters, incorporating regions of different braid density and/or material characteristics, and methods of manufacture therefor.
The use of intravascular catheters for treatment of the body is well known in the field of medicine. The need for a choice of catheter sizes and types has grown rapidly as the techniques for their use have been greatly improved and the types of medical uses have expanded quickly. One such catheter is a guide catheter which includes a tubular member having a lumen therethrough. Guide catheters are commonly used in diagnostic and treatment techniques related to vascular disease such as angioplasty.
A guide catheter is typically inserted into the femoral artery and routed to a location near a treatment or diagnostic site through the aorta over the aortic arch to the ostium of a target vessel. The guide catheter provides a conduit so that fluid or another medical device can be delivered easily to the proximate location of treatment via the lumen of the guide catheter. Prior art catheters often include a tubular member including a pair of congruent tubes, the inner one defining the lumen. A hub is connected at the proximal end of the tubes, which in addition to providing access to the lumen for fluids and the like, is often used to input torque and other necessary pressures to the tubes during their placement within the body. A tip of a selected design is placed at the distal end of the tubes.
In order for the physician to place the catheter at the correct location in the vessel, the physician must apply longitudinal and rotational forces. The catheter must be rigid enough to transmit sufficient force from the proximal end to the distal end, yet flexible enough to navigate the bends in the blood vessel. Further, the catheter must be torsionally rigid to transmit the applied torque and radially rigid to resist kinking. One way to accomplish a balance between longitudinal rigidity and flexibility, while insuring sufficient torque and radial strength, is to provide a support member in the catheter shaft. Typically, the support member is provided between an inner tube and an outer tube to form the catheter shaft.
The support member is often a braid of metal wires or the like. The performance criteria of a catheter can be affected by altering the density (i.e., pic count) of the braid. Specific performance criteria which can be altered include shaft stiffness, curve support, and kink resistance. Altering the braid pic count can affect shaft stiffness by changing the amount of polymer in the catheter shaft and the degree of interstial bonding between the polymer and the inner tube. Altering the braid can also affect curve support in a similar manner. Polymer in the shaft forming the curve provides support and shape memory. In addition, an optimal degree of braid density is required in the curve to provide a degree of flexibility so that the catheter shaft can align coaxially to the engaged artery. Finally, altering the braid pic affects kink resistance. Increasing braid pic will normalize the braid angle to the catheter surface and increase the amount of reinforcing wire in the shaft.
It is possible to construct a device that is very rigid to obtain the correct amount of shaft stiffness and curve support. However, the resulting device may track poorly, be traumatic to the patient""s arteries and kink easily due to its rigidity. Similarly, it is possible to construct a very flexible device to increase trackability, limit the trauma the device imparts to the blood vessels and limit kinkability. However, the device then may become too flexible to provide sufficient shaft stiffness and curve support.
The present invention overcomes many of the disadvantages associated with the prior art by varying the braid density in specific regions of the catheter, thereby optimizing shaft stiffness, curve support and kink resistance. Further, the present invention contemplates placing a number of segments, each having selected mechanical characteristics, at desired locations along the length of the catheter. Accordingly, the present invention may allow both the mechanical characteristics and the braid density to be independently varied along the length of the catheter to help reduce catheter back-out and maximize catheter performance.
In one illustrative embodiment of the present invention, a catheter shaft having a first region and a second region is provided. A support member extends along at least a portion of the catheter shaft including along the first region and the second region. The support member has a first portion that corresponds to the first region of the catheter shaft and a second portion that corresponds to the second region of the catheter shaft. The density of the support member is changed by changing the diameter of the support member in the first portion relative to the second portion. Thus, the first portion of the support member may provide different torsional rigidity, flexibility, and radial strength to the catheter shaft relative to the second portion.
Preferably, the support member is braid that is disposed between an inner layer and outer layer of the catheter shaft. To increase the diameter of the braid, it is contemplated that the inner layer may have an increased diameter in the first region relative to the second region. This may be accomplished in any number of ways, including providing an annulus or short tubular segment of material around the inner layer adjacent the first region, or using a sleeve to selectively increase the density of the braid in the first region, as more fully described below.
It is also contemplated that the outer layer of the catheter shaft may include two or more segments, wherein at least one of the segments includes a material that has different mechanical characteristics than another one of the segments. For example, the catheter may include a first tubular section and a second tubular section, wherein the first tubular section includes a plastic material that has one or more different mechanical properties than the plastic material of the second tubular section. As more fully described in U.S. patent application Ser. No. 08/800,927 filed Feb. 13, 1997, entitled xe2x80x9cGuide Catheter Having Selected Flexural Modulus Segmentsxe2x80x9d, selected polymers having different characteristics may be used for various regions of the catheter. This may allow the rigidity of the catheter to be increased in discrete segments, thereby increasing the curve resistance while maintaining the flexibility of the catheter. Accordingly, the present invention may allow both the polymer characteristics and the braid density to be independently varied along the length of the catheter for optimal catheter performance.
The present invention also contemplates a number of methods for forming a catheter having a support member with various braid densities along its length. One illustrative method for forming a catheter having an inner tube and a support member includes the steps of: providing the support member over the inner tube; causing a first region of the support member to have a first diameter, wherein the first region has a proximal end and a distal end; securing the support member relative to the inner tube proximate the distal end of the first region; causing a second region of the support member to have a second diameter, wherein the first diameter is different from the second diameter, and wherein the second region overlaps at least a portion of the first region; and securing the support member relative to the inner tube proximate the distal end of the second region. The support member may be secured to the inner tube using any number of techniques including using a suitable adhesive or an annulus of heat shrink tubing.
More specifically, the above method for forming a catheter having an inner tube and a support member may includes the steps of: sliding the support member distally over the outer surface of the inner tube; sliding a first sleeve having a distal end over at least a portion of the support member until the distal end of the first sleeve reaches a first location, the first location being distal of the proximal end of the inner tube; securing the support member relative to the inner tube proximate the first location; removing the first sleeve; sliding a second sleeve having an inner diameter that is less than the inner diameter of the first sleeve over the support member until a distal end of the second sleeve reaches a second location, wherein the second location is proximal of the first location; and securing the support member relative to the inner tube proximate the second location.
Another illustrative method of the present invention for forming a catheter having an inner tube and a support member includes the steps of: forming an inner tube having a first region and a second region, wherein the first region has a first outer diameter and the second region has a second outer diameter; sliding the support member distally over at least a portion of the inner tube including over the first region and the second region; tensioning the support member against the first region and the second region; and providing an outer layer over the support member. Preferably the first region of the inner tube has an increased outer diameter relative to the second region, and is formed by providing an annulus or tubular segment of material around the inner tube over the length of the first region.
These and other various advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof However, for a better understanding of the invention, its advantages and the objects obtained by its use, reference should be made to the drawings which form a further part hereof and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the present invention.